The invention relates to a process for improving the flavor of secondary coffee extracts, especially for the production of soluble, i.e. instant coffees.
In the production of coffee extracts, first a primary extract from roast coffee is obtained under mild temperature and pressure conditions. Said primary extract usually has a high quality nearly reaching that of instant coffee infusions used in households. This primary extraction can for example be conducted in a percolator with hot water.
The primary extraction step has a yield of only 20 to 30% and it was therefore quite obvious to increase the yield by means of a second extraction step. This additional extraction is conducted under more rigorous temperature and pressure conditions (EP-A-151 772). However the resulting secondary extract has a high acid content which is found to be unpleasant as regards flavor and furthermore, said extract has unpleasant flavor notes which are often called "hydrolytic flavor". These unpleasant notes impede the quality of the final product and add to the typical taste of soluble coffee which is different from ordinary roast coffee infusions.
Consequently, a number of methods for treating secondary coffee extracts have been proposed. EP-A-78 121 discloses for example the removal of undesirable substances from secondary coffee extract by means of a liquid/liquid-extraction with a plant oil. EP-A-78 618 suggests to treat secondary extracts with solid organic polymeres and DE-A-34 00 768 to treat them with low-alkalinity ion-exchangers.
DD-A-268 151 relates to a process for stabilizing the aroma of ground coffee which is supposed to result in a roast coffee with improved organoleptic properties and a higher storage stability. It is proposed to treat the ground roast coffee with adsorption agents such as finely or coarsely pored silica gels and synthetic or naturally occurring zeolites.
EP-A-13 451 discloses a process for removing caffeine from aqueous solutions of green or roasted coffee beans with a certain crystalline zeolitc molecular sieve of the Y-type, namely the UHP-Y, which has a high selectivity for caffeine.